The present relates generally to refrigeration air conditioning systems, and more particularly to an air conditioning system wherein liquid refrigerant accumulator-heat exchange means utilize a relatively cool mixture of liquid and vaporous refrigerant from the evaporator in a heat exchange relationship with hot liquid refrigerant discharged from the condenser for significantly sub-cooling this hot liquid refrigerant prior to the partial evaporation thereof in the evaporator for providing the aforementioned mixture and a air conditioning system with a liquid over-feeding operation.
Refrigeration air conditioning systems each include basic components defined by a compressor, condenser, expansion device, and an evaporator that are serially interconnected by a conduit or piping arrangement used for the circulation of refrigerant in liquid and vaporous form through the system. In operation of such systems, relatively cool refrigerant in gaseous or vapor form is compressed to an elevated pressure and temperature in the compressor with the temperature of the vaporous refrigerant increasing with increasing pressure due to work by the compressor. The resulting relatively hot compressed vaporous refrigerant is then condensed to liquid in the condenser with the heat given off by the condensing vapor being removed from the condenser by employing a heat exchange medium such as a moving stream of air or water. The condensed liquid refrigerant is then passed through an expansion device where the pressure of the liquid is substantially decreased. This expansion of the liquid refrigerant also results in some vaporization of the liquid refrigerant which cools the liquid refrigerant due to latent heat of vaporization. In the evaporator, the liquid refrigerant is converted to saturated vapor by absorbing heat from a heat exchange medium such as a moving stream of air or water passing through the evaporator. The saturated refrigerant vapor discharged from the evaporator is at essentially the same or at a lower pressure than the liquid refrigerant entering the evaporator and is transported to the compressor for recompression and recycling of the refrigerant through the system.
In such air conditioning systems it is necessary to prevent liquid refrigerant from being introduced into the compressor in order to protect the compressor from "liquid slugging back" effects which significantly detract from the integrity of the compressor. Efforts to assure that essentially only vaporous refrigerant, preferably saturated vaporous refrigerant, is introduced in the compressor the evaporators are usually appropriately sized so that the evaporator coil arrangement therein providing for the direct expansion of the liquid refrigerant entering the evaporator is provided with a dry coil region, i.e., free of liquid refrigerant, and corresponding to about ten percent of the evaporator coil volume for assuring that all or essentially all of the liquid refrigerant is evaporated in the evaporator. This dry coil region in the evaporator does not provide for any meaningful cooling of the heat exchange medium passing through the evaporator and thus adversely affects the overall system effectiveness of the air conditioning system.
Additionally, some air conditioning systems have been fitted with suction line heat exchangers which are utilized to exchange heat between the hot condensed liquid refrigerant or another liquid such as water and the vaporous refrigerant discharged from the evaporator for assuring that any liquid refrigerant contained in the suction lines is converted to vapor. The use of such a suction line heat exchanger also causes the vaporous refrigerant in the suction line to be superheated but such superheating of the gaseous refrigerant directly affects the temperature of the vaporous refrigerant discharged from the compressor and requires that the compressor provide additional work for compressing the vaporous refrigerant to the required pressure necessary for effecting the condensation thereof in the condenser. In as much as the dry coil region of the evaporator normally assures that little if any liquid refrigerant enters the suction line, the evaporation of any liquid present in the suction line by using suction line heat exchangers will provide compressor protection.
The type of refrigerant employed in conventional air conditioning systems such as generally described above is of considerable importance in determining the cooling efficiency of the system. A commonly used refrigerant of the many available refrigerants is refrigerant-12 formed of dichlorofluoromethane (CC1.sub.2 F.sub.2) and which is a medium pressure/medium capacity refrigerant. Refrigerant-22 formed of monochlorodifluormethane (CHC1F.sub.2) provides an alternative to refrigerant-12 but is a high pressure/high capacity refrigerant which requires some system modifications for handling such a refrigerant. However, the use of refrigerant-12 and refrigerant-22 as well as other refrigerants which contain chlorine have been found to be environmentally unacceptable since the chlorine component is considered to be a principal involved in the ongoing destruction of the protective ozone layer encompassing the earth. While refrigerant-22 reportedly causes only about five percent as much damage to the ozone layer as a similar volume of refrigerant-12 discharged into the atmosphere at the surface of the earth, the utilization of either of these refrigerants in the manufacture of new air conditioning systems as well as in repairing or modification of existing air systems is presently discouraged and is expected to be banned altogether by legislation.
Recently, developments in refrigerants which are expected to be environmentally acceptable are chlorine-free and include the refrigerant-134a formed of tetrafluoroethane (CF.sub.3 CH.sub.2 F). It is anticipated that the use of such a chlorine-free refrigerant will be soon required in the manufacture and the repair of air conditioning systems such as used in the transportation industry, refrigerators, freezers, building cooling applications, and in heat pump assemblies.
However, it has been found that the utilization of refrigerants other than refrigerant-12 and refrigerant-22 in existing air conditioning systems result in considerable reduction in system efficiency. For example, in a conventional automotive air conditioning system the use of refrigerant-134a in place of refrigerant-12 results in a decrease in system efficiency of about six percent.